1. Field of the Invention
The present invention relates to a management system of rechargeable battery (or secondary cell, storage battery) system and a method for managing thereof. Especially, the present invention relates to a system and a method for managing a rechargeable battery which is used in various portable electrical equipment such as a wireless radio, an audio tape player, a camera, an electric lamp and so on wherein the termination voltage is equalized using parallel discharging method before charging the rechargeable battery so that the durability of the rechargeable battery is expanded and the efficiency of the charging is enhanced.
2. Description of the Background Art
The rechargeable battery so called a secondary battery or a storage battery is being produced and sold in various types and sizes. The typical type of the rechargeable battery is a nickel cadmium (NiCd) type, a lead-acid type, a nickel metal hydride (NiMH) type, a lithium ion (Li-ion) type, a lithium polymer type, an alkaline type and so on according to its components. These rechargeable batteries should be charged using the appropriate charging method in order to be used for full durability. For example, the NiCd type is preferred to be fully discharged periodically before using it. The Li-ion type used in notebook computers video cameras, mobile telephones and so on is preferred to be charged before it is discharged up to the discharge terminal voltage. The lithium polymer type used in the small electrical devices, the medical equipment, computers and so on, should be always in a charged state before it is exhausted by discharge. The durability of the lithium polymer type could be shortened, if it is fully discharged like nickel cadmium type. As mentioned above, despite the difference in usage direction according to the different types, many rechargeable batteries are not used for full durability and wasted as the users misuse them. The wasted rechargeable batteries are one factor of the environmental pollution, especially, the Nixe2x80x94Cd type battery causes a serious environmental problem as there is toxic in the cadmium. Many countries use their budget and carry out the educational campaign for collecting the used batteries. Furthermore, wasting of the rechargeable batteries is a dissipation of the natural resource.
Hereinafter, we will explain about the Nixe2x80x94Cd and NiMH type chargeable batteries which are deeply related with the present invention. Because the Nixe2x80x94Cd type costs less and is easy to store and deliver as well as being rechargeable in a short time, it is still used in many fields even though it was developed long time ago. Furthermore, it is the best kind of the rechargeable battery in the industrial field because the discharging energy per time is big, the durability is long and it can be recharged many times than others. It is applied to electrical devices which need big electrical energy such as a flash of a camera, a cordless telephone, a radio, a satellite auxiliary battery, a motor driver, a portable and wireless vacuum cleaner, a diving light, a radio controlled model (car, airplane and ship) and so on. If the Ni-type battery is recharged without deep discharging, the recharging time is reduced because of the memory effect in which the rechargeable capacitance is reduced by crystalizing the un-reacted active materials. Generally, the rechargeable batteries are used in serial connection with many cells except for the case of using only one cell. In this case, the cells are discharged so that they are in a different energy state. After the cells are used in a serial connection so that, they are discharged in different energy states, the energy state of the cells also become different if they are recharged. If the group of the cells are discharged and recharged many times, then the termination voltage of some cells could be lower than 0.1 volt. In this state, if the user further uses these cells, then the electrical potential is reversed so that these cells are in the battery reversal state. If the secondary battery which comprises many rechargeable cells having different energy states are connected in serial is recharged, then the recharging is stopped when one cell having the most high energy state sends the termination signal of recharging to the charger despite the cell having the lowest energy state is not charged yet. On the other hand, in the case of the secondary battery including an over discharged cell, the other cells reach over charged state before the over discharged cell is completely charged. That is, the status of some cells comprised in the secondary battery moves back and forth between the uncompleted charging state and the over discharging (or battery reversal) state. At the same time, the status of the other cells move back and forth between the completed charging state and the uncompleted discharging state. Therefore, all the cells are damaged.
The performance of the Ni-type rechargeable battery can be enhanced by deep discharging periodically so that the crystallized electrolytes are removed. However, the secondary battery generally comprises many cells connected in serial in order to obtain the wanted electric voltage for using the electrical device. Under this state, if the secondary battery is discharged for management, then some cells of the secondary battery can be over discharged or be in the battery reversal state. That is, it is hard to recover or to equalize the cells using the discharging method in the serial connection. In order to solve the above problem, the individual discharging method is suggested in the U.S. Pat. No. 3,980,940, as shown in FIG. 1. This conventional invention suggests a method for managing the secondary battery in which the cells are equalized by deep discharging individually before they are recharged in serial connection. The rechargeable batteries (cells) 1a, 1b, 1c and, 1d are connected in serial connection. The recharging means 11 is connected to the rechargeable batteries 1a to 1d. The discharging means 21 comprising the electrical load means 23a, 23b, 23c and 23d and discharging blocking switch 25a, 25b, 25c and, 25d is connected with the rechargeable batteries 1a to 1d individually. That is, the electrical load means 23a to 23d and the discharging blocking switch 25a to 25d are connected to the rechargeable batteries 1a to 1d, respectively. In this conventional invention, each cell 1a to 1d is discharged individually using the discharging means 21 after the cells are recharged in serial connection using the recharging means 11. However, according to the conventional invention, the amount of the energy wastes during individual discharging is very big and it takes a long time to discharge all the cells in different energy state should be fully discharged.
There is a need for a system and a method in which the rechargeable batteries are equalized without the deep discharging of each battery. After that, the charging can be performed for a shorter time period. One object of the present invention is to provide a system and a method for managing the rechargeable batteries in which they are protected from the being damaged due to over discharge or over charge by equalizing the energy difference of the each rechargeable battery. Another object of the present invention is to provide a system and a method for managing the chargeable batteries in which the rechargeable batteries are discharged in parallel connection for equalizing the energy states of the each battery and then they are recharged in serial connection, so that the discharging efficiency is maximized and the charging is performed quickly.
In order to obtain these objects, the present invention provides a managing system for rechargeable battery comprising a plurality of a rechargeable unit batteries, a closed loop circuit method which connects the cells in parallel connection electrically, an electrical load means having regular voltage which is the sum of the maximum output voltage among the plurality of cells and being in parallel connection with the rechargeable cells which are connected in parallel with the closed loop circuit method, a rechargeable battery manager including a discharging blocking switch inserted between the plurality of cells and the electrical load means in order to cut off the current flowing in the electrical load means in case it reaches the discharge termination voltage of the plurality of rechargeable cells. In addition, the present invention provides a method of managing the rechargeable battery including a step of discharging for a certain time period by parallel connecting the plurality of rechargeable cells which have different energy level using the battery manager for discharging. The present invention also provides a plurality of rechargeable cells, a closed loop circuit means connecting the rechargeable cells, a selection switch connected to the closed loop circuit means which allows the cells to be connected either by parallel connection or serial connection, an electrical load means having regular voltage which is the sum of the maximum output voltage among the plurality of cells and being in parallel connection with the rechargeable cells which are connected in parallel with the closed loop circuit method and a manager for rechargeable battery including a voltage applying means which provides rechargeable voltage between the both electrodes of the cells connected in the serial connection in case the cells are in serial connection at the same time the current flowing in the electrical load means is cut off by the switch means. Finally, the present invention provides a managing method for rechargeable batteries including steps of discharging the plurality of rechargeable cells which have different energy level for a certain time period by connecting them in parallel connection using the manager for chargeable cells and charging the plurality of the rechargeable cells by connecting them in serial connection after the above mentioned parallel discharge.